The Z disc is a dense protein structure that connects the thin filaments of a sarcomere. The filaments are composed of actin and are flanked by the Z discs on either side. The Z disc is an important component of the muscle's contractile apparatus, and it is responsible for transmitting the force generated by the myofilaments to the tendons and bones.

The Z disc is composed of a variety of proteins, including α-actinin, desmin, and vinculin. These proteins help to crosslink the actin filaments and to maintain the structural integrity of the disc. The Z disc also contains a number of other proteins that are involved in the regulation of muscle contraction, including tropomyosin and troponin.

The Z disc is a critical component of the muscle's contractile apparatus, and it is essential for the proper functioning of the muscle. Without the Z disc, the actin filaments would not be able to transmit force to the tendons and bones, and the muscle would not be able to contract.